AUSTIN (KXAN) — It all started as a joke.

A Facebook post calling on people to storm Area 51 — in search of aliens.

But after a huge response online, authorities are now wondering how many people will actually show up. Two million people have RSPD’d so far.

MORE: US Air Force warns against joke event to ‘storm Area 51’

A recent survey found that a majority of Americans believe the government knows more than they’re telling us.

“So clearly there are aliens out there,” said Seth Shostake, senior astronomer at SETI Institute, or the Search for Extraterrestrial Intelligence Institute. “I think it’s a pretty strong argument, but we don’t have the proof of that and I don’t think it’s stocked up in Southern Nevada. Honestly, I don’t.”

The U.S. Air Force claims the 60 square miles in the desert are used for aircraft testing and nothing more.

Do you believe it?